The present invention relates to an active-matrix liquid crystal display device, and particularly to a liquid crystal display device of the so-called in-plane field type.
In color liquid crystal display devices of the in-plane field type, one or both of two transparent substrates placed opposite to each other, with a liquid crystal layer disposed in between, have display electrodes and reference electrodes arranged in areas on the sides of the liquid crystal corresponding to unit pixels, and an electric field parallel to the transparent substrate surface is produced between the display electrodes and the reference electrodes to modulate light passing through the liquid crystal layer.
Such a color liquid crystal display device can produce a picture that can be recognized at a wide viewing angle and has become known for its excellence in the so-called wide angle visual field.
Liquid crystal display devices with the above configuration are described in detail, for example, in the Published Japanese Translation of PCT International Publication for Japanese Patent Application No. 505247/1993, Japanese Patent Publication No. 21907/1988, and Japanese Patent Laid-Open No. 160878/1994.
It has been pointed out that liquid crystal display devices of this configuration, however, have a problem in that an undesired electric field produced from the video signal line changes the electric field between the display electrodes and the reference electrodes, causing so-called vertical smear extending along the video signal line on the display surface. A known means to solve this problem involves the use of a shield electrode on the same substrate close to the video signal line (see Japanese Patent Laid-Open No. 202127/1994).
Liquid crystal display devices thus structured, however, have a problem in that, because the shield electrode is provided on the same substrate, the capacitance between the shield electrode and the signal electrode is large, the load on the drive circuit becomes too heavy, and the power consumption or the size of the drive circuit becomes too large.
Liquid crystal display devices thus constructed have another problem in that, because opaque electrodes are formed like a comb, the percentage of the pixel area occupied by the opaque metal is high, and so the aperture ratio cannot be increased.
Further, because a voltage is applied to the reference electrodes formed in individual pixel areas through common stripe-shaped reference signal lines extending in a row or column direction, the waveform of the applied voltage becomes dull from the signal supply portions of the reference signal lines toward the far ends of the reference signal lines, with the result that a brightness gradient or so-called horizontal smear occurs with the reference signal lines on the display surface.
The present invention has been accomplished to avoid these circumstances and an object thereof is to provide a liquid crystal display device that minimizes so-called vertical smear and reduces power consumption and the size of the peripheral circuits.
Another object of this invention is to provide a liquid crystal display device having an improvement in the so-called aperture ratio.
Still another object of this invention is to provide a liquid crystal display device in which what is generally-called a brightness gradient and also the horizontal smear are suppressed.
A further object of this invention is to provide a liquid crystal cell with a low reflectance.
Representative aspects of this invention disclosed in this specification may be briefly summarized as follows.
An active-matrix liquid crystal display device, which is applicable to the present invention comprises transparent substrates opposed to each other; a liquid crystal layer interposed between the opposed transparent substrates; pixel areas arranged on the surfaces of the transparent substrates on the liquid crystal side; and display electrodes, reference electrodes, scan lines, video signal lines and active devices arranged in the pixel areas; wherein a voltage is applied between the display electrodes and the reference electrodes to produce an electric field parallel to the transparent substrates in the liquid crystal layer to modulate light passing through the liquid crystal layer. A first aspect of the invention is characterized in that, on one of the transparent substrates, the reference electrodes are arranged on both sides of the video signal lines, and on the other transparent substrate, a shield electrode is formed to cover in plan view the video signal lines in the pixel areas and a part of the reference electrodes on both sides of the video signal lines.
An active-matrix liquid crystal display device which comprises: transparent substrates opposed to each other; a liquid crystal layer interposed between the opposed transparent substrates; pixel areas arranged on the surfaces of the transparent substrates on the liquid crystal side; and display electrodes, reference electrodes, scan lines, video signal lines and active devices arranged in the pixel areas; wherein a voltage is applied between the display electrodes and the reference electrodes to produce an electric field parallel to the transparent substrates in the liquid crystal layer to modulate light passing through the liquid crystal layer; the aspect of the invention is characterized in that, on the other transparent substrate opposed to the one transparent substrate formed with the video signal lines, a shield electrode is formed completely overlapping the video signal lines in plan view and is formed integrally with the reference electrodes; and the video signal lines for allowing the display electrodes to function and the reference signal lines connected with the reference electrodes are completely superimposed when seen in plan view.
In accordance with the invention, the shield electrode is electrically connected to the light shielding layer having apertures only at the pixel areas or is integrally formed with the light shielding layer.
In the active-matrix liquid crystal display device which comprises: transparent substrates placed opposed to each other; a liquid crystal layer interposed between the opposed transparent substrates; pixel areas arranged on the surface of one of the transparent substrates on the liquid crystal side; display electrodes, scan signal lines, video signal lines and active devices arranged in the pixel areas; and a conductive light shielding layer formed in matrix, provided in the pixel areas on the other transparent substrate and supplied with a reference signal; wherein a voltage is applied between the light shielding layer and the display electrodes to produce an electric field having a component parallel to the transparent substrates to modulate light passing through the liquid crystal layer; the third aspect of the invention is characterized in that the light shielding layer has a multilayer structure comprising a layer with a reflectance of 10% or less on the transparent substrate side and a highly conductive layer on the liquid crystal layer side; that a backlight unit is disposed on the side of the transparent substrate provided with the display electrodes, the scan signal lines, the video signal lines and the active devices, opposite to the liquid crystal layer; and that the transparent substrate provided with the display electrodes, the scan signal lines, the video signal lines and the active devices has thereon a connection terminal for supplying the reference signal to the light shielding layer and a conductive layer fox electrically connecting the connection terminal to the light shielding layer.
In accordance with the first aspect of the present invention, because the video signal lines and the reference electrodes adjacent to the video signal lines, both formed on one of the transparent substrates, are completely superimposed, in plan view, by the shield electrode formed on the other transparent substrate, unwanted electric lines of force generated by the video signal lines are terminated at the shield electrode and the reference electrodes adjacent to the video signal lines, thus preventing the electric field between the display electrodes and the reference electrodes from varying depending on the video signal, and greatly minimizing the vertical smear.
Further, because the shield electrodes are formed on the substrate opposite to the video signal lines, the shield electrodes and the video signal lines are spaced more from each other by the thickness of the liquid crystal layer, so that the capacitance between the shield electrodes and the video signal lines is reduced. This prevents the load on the drive circuit from increasing, minimizes power consumption and reduces the size of the drive circuit.
In accordance with the second aspect of the present invention, because the video signal lines for allowing the display electrodes to function and the reference signal lines connected with the reference electrodes are formed to completely overlap each other, when seen in plan view, the effective pixel areas can be increased, thus improving the so-called aperture ratio.
Further, because the reference electrodes are so formed as to be electrically connected to the light shielding layer having apertures only at the pixel areas, a voltage is applied through a low resistance to the reference electrode in each pixel area. As a result, the reference signal waveforms can be prevented from becoming dull, thus minimizing what is generally called a brightness gradient and the horizontal smear.
Furthermore, the third aspect of the present invention has the features of the first and second aspects combined and can reduce the reflectance of the liquid crystal display device.